The Planck era
We now have two different but related dictionaries for describing what happens at the Planck scale: string theory and LQG. And that means we now have a way to describe conditions in the universe during and just after the Planck era. Here is a story of what the Planck era might have looked like and what it might tell us about cosmogenesis, told in the combined language of string theory and LQG.
The nothing state: In many ways, the “beginning” of the Planck era is not a logical concept. Nor does it have a real name, for any name presupposes a time, place, or quality, none of which can apply here. According to physicist Daniele Oriti of the Max Planck Institute for Gravitational Physics in Potsdam, Germany, this primitive state of Nothing may have consisted of ingredients that were not at all resembling space or time.
But as Nobel laureate and physicist Frank Wilczek once said, “The reason there is something rather than nothing is that nothing is unstable.” This instability led to a phase change in the state of nothing. In LQG parlance, nothingness has been converted into something: a plenum of countless elementary Planck volume nodes. It happened perhaps in the same way that a cloud of water molecules in a gas changes phase into a cloud of liquid droplets – rain – when the temperature drops.
Geometrogenesis: Our new State of Something, made up of space droplets (nodes), did not remain random for long. The nodes were embedded in link networks that defined the dimensionality of the spin (N) network, which in turn defined the number of nearest neighbors to each node. According to Lee Smolin – one of the developers of LQG – from the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, the energy available to maintain these links could have been so enormous that the Planck volumes could have been elements of a space with much more than the supposed 11 dimensions of the Bulk. But even this state was unstable and caused a second phase change as the available energy decreased.
Imagine a very particular landscape. There are mountains where the connections are numerous (large number of dimensions). These slots require huge amounts of energy to maintain. And there are valleys (with less dimensions), where less energy is needed. Phase changes occur when it is more favorable for a system to exist at a lower energy than at a higher energy. This suggests that spaces with a large number of dimensions tend to become spaces with less energy and fewer dimensions. The change occurs through a process called quantum tunneling.
So we can imagine that a second phase change occurred when the new N-dimensional something state tunneled to one of those lower energy states of the spin networks with less bonding between the knots. All but 11 of the original many dimensions disconnected from nodes and disappeared. This may have formed the geometric basis of the Bulk in string theory.
Compaction: According to string theory, there must have been an event, process, or circumstance in which seven of the 11 volume dimensions were compacted to create the specific details of the standard pattern in our four-dimensional universe. We can imagine this as a third phase transition which, in the parlance of LQG, caused the links representing seven of the 11 dimensions to develop closed spaces, each with a specific geometry. Of the remaining four dimensions, three have formed space-like three-dimensional spin networks, or branes.
Chronogenesis: A fourth phase transition occurred as one of the four spatial dimensions of the Bulk morphed into a time dimension that tracked changes occurring between spin network configurations to produce spin foams. Stephen Hawking and James Hartle proposed this idea in 1983 to solve the problem of the origin of time in cosmology. They called it the Borderless Proposal because it eliminated the need to discuss what happened before the Big Bang. Essentially, they said, the universe has no (beginning) boundary, just as there is no point north of the North Pole. Once a dimension emerged as the direction of a succession of spatial states (branes in string theory; spin networks in LQG), it established cause and effect, and the Big Bang unfolded. product.
Cosmogenesis: At first, the scope of the Big Bang was limited to the Planck scale as bubbles of new space-time emerged from within the larger network of purely spatial dimensions. It was an incredibly turbulent time, perhaps resembling the topsy-turvy chaos of what theoretical physicist John Wheeler called quantum space-time foam. Collections of nodes came together to form the first primordial objects – quantum black holes – but these quickly decayed into individual nodes. Other collections of nodes adopted a wave-like behavior and passed through the spin foam network as gravitons.
Structures larger than Planck’s scale began to form rope-like objects made up of nodes organized along one dimension of space. Together with the information (provided by their links) about the seven compact dimensions, they took on the properties of individual particles that we recognize in the Standard Model. Huge sets of these strings began to behave like organized quantum fields. How one string interacted with another is described by how a huge collection of nodes turned into another collection as part of a spin foam pattern.
During all these phase transitions, the amount of information encoded in the network of nodes increased steadily. This had a profound effect on the precision with which mathematical relationships between nodes along the emergent time axis could be specified. These relationships are what we call the physical laws of nature and include how we describe gravity and the details of the Standard Model. So, during this last stage of the Planck era, not only time emerged, but also the laws of nature now operating in our spacetime.
In his book The Spirit of GodPaul Davies notes that “[Prior to] a second after the Big Bang there was less space and less information, so the math was in a cruder form. The computing power of the universe at the time of Planck was practically nil. All the math would have been meaningless and the laws would have been almost impossible to state.
At first the physical laws were very roughly specified, but over time and as the information available increased, these models became more detailed. Essentially, the physical laws of our universe emerged from the growing informational content of the universe within which those laws could be defined. Once these patterns emerged and became more accurate, the progression of the Big Bang became richer in specific patterns of how particles interact in space and time.
The bigger picture
If we were to take a step back and look at the big picture in Planck’s time, we could envision a succession of bubbles within bubbles. The largest of these encompasses the domain of spin networks in which other numbers of dimensions exist. In some of these bubbles, space has crystallized into 11 dimensions. We call our 11-dimensional bubble the Bulk. But there may be other Bulks with less or more than 11 dimensions.
Additionally, in our Bulk bubble, one of the dimensions passed through time and served to organize the 3D branes (spin networks) into a recognizable chronological order: our 4D spacetime. Another transition compacted seven of the spatial dimensions, giving rise to our specific Standard Model particles and fields. Only the exact geometry of compact 7D spaces defines what the standard model will look like for a given universe. But because String Theory provides 10,500 ways to do this, there are many different 11-dimensional Bulks, each with its own way of compacting those seven dimensions.
Taken together, they are called the Landscape. You may know it as the idea of a multiverse. Continuing the analogy of our universe as a 4D collection of book-like branes, then the Vrac is like a giant library containing an infinite number of these book universes, each with different geometries for these compact spaces, leading to different patterns standard.
Back in our own space-time bubble, now much larger than the Planck scale, the background network of nodes defining four-dimensional spin foam began to look smoother and smoother at larger scales. large as the universe grew older. After a while, inflation happened, ending about 10-34 seconds after the Big Bang…and here we are!
Of course, this whole story is highly speculative, even fanciful. It is based on theories or bits of theories that remain largely unproven – or perhaps, one shudders to think, even unprovable. But our search for the origin of the universe is the result of who we are as sentient beings.
Together with observations, we can continue to create and improve universe origin stories that answer many older questions while providing new ones for future generations to explore and test.